Instant Rice to Clean Grinders

 https://www.bhg.com/should-you-clean-your-coffee-grinder-with-rice-7561896

Coffee connoisseurs online have discovered that dry instant rice addresses this issue. Dry, precooked rice has softened to a brittle texture similar to coffee beans and is super effective at cleaning burr grinders without causing any damage. If you don’t want to spring for instant rice, you can make it at home by dehydrating cooked rice, although the time commitment is much steeper.

This Youtuber actually tested all the different methods and tested the final result with actual coffee tasting.

The cheapest is just normal cooked rice that is air dried. A little bit harder than dehydrated cooked rice and pre-booked instant rice but should still work as well in cleaning the grinder.